1. Field of the Invention
The present invention relates to a method for transmitting data, and more particularly, a method for transmitting data in a wireless communication system and a system thereof.
2. Description of the Prior Art
Long Term Evolution (LTE) is being developed by the 3rd Generation Partnership Project (3GPP) and moving towards creating more efficient communication systems. In 3GPP TS 36.321 specification for LTE MAC protocol, dynamic resource allocation for uplink transmissions has been introduced for improving the efficient utilization of the radio resources between a user equipment (UE) and a Node B, i.e. a base station in an Evolved Universal Terrestrial Radio Access Network (E-UTRAN). With the dynamic resource allocation, the radio resources are allocated only when the UE has data to transmit so that the radio resources for data transmission can be saved.
As today's applications for electronic systems grow at ever-increasing rates, the demand for better communications performance is never ceasing. Standards for various technologies such as the 3rd Generation Partnership Project (3GPP) High-Speed Packet Access (HSPA) and Long Term Evolution (LTE) work towards creating more efficient communication systems. For example, dynamic resource allocation for uplink transmissions has been introduced in the 3GPP TS 36.321 standard, for communicating between a user equipment (UE) such as a mobile station or a mobile handset, and an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) base station. Dynamic resource allocation utilizes radio resources more efficiently, where radio resources are allocated only when the UE has data to transmit. But a drawback becomes clear when insufficient radio resources are allocated by the E-UTRAN: the UE must request for resources to be allocated and wait for the uplink resource allocation, and this causes a delay before its data can be transmitted, slowing down the overall communication between the UE and the E-UTRAN. Fast allocation of uplink resources may be required when the UE and E-UTRAN are in an active downlink session but there is a need to transmit uplink data. Fast allocation of uplink resources may also be required when uplink data has been unsuccessfully received and needs to be retransmitted. The E-UTRAN informs the UE of the status of received data packets via STATUS PDUs, which contain positive and/or negative acknowledgements of RLC PDUs. The STATUS PDU can be sent in response to a polling request from the UE, as disclosed in RLC protocol specification 3GPP TS 36.322 v8.2.0: “The receiving side of an AM RLC entity shall trigger a STATUS report when it receives a RLC data PDU with the P field set to “1” and the HARQ reordering of the corresponding RLC data PDU is completed”.
FIG. 1 shows an exemplary signaling diagram 1000 illustrating an uplink data transmission from a User Equipment (UE) 1100 to an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) 1200 in an LTE system, according to the current convention. The UE 1100 comprises a Radio Link Control (RLC) layer 1110 and a Medium Access Control and Physical (MAC/PHY) layer 1120. Similarly, the E-UTRAN 1200 comprises an RLC layer 1210 and a MAC/PHY layer 1220. In the mentioned figure and example, the RLC 1110 of the UE 1100 initiates a transmission of RLC data PDUs 1-5 (indicated at 1300), and sends a data transmission request to the MAC/PHY layer 1120 (indicated at 1310). The MAC/PHY layer 1120 notes that an uplink resource is already allocated (indicated at 1320) for the UE 1100, and thus sends a confirmation signal to the RLC 1110 so as to confirm that data transmission may begin (indicated at 1330). Following this, the RLC 1110 respectively sends the five RLC data PDUs, i.e. RLC data PDUs 1, 2, 3, 4 and 5, (indicated at 1340a-e) to the MAC/PHY 1120. After receiving the five RLC data PDUs, the MAC/PHY 1120 converts them as MAC PDUs and then sends them to the MAC/PHY layer 1220 of the E-UTRAN 1200 respectively. In addition, the MAC/PHY 1120 packages a Buffer Status Report (BSR), which indicates the UE transmission buffer is now empty, into the MAC PDU 5 so as to inform the E-UTRAN 1200 that the information to be sent has been sent. Upon receiving the empty buffer information, the MAC/PHY 1220 closes the uplink resource (indicated at 1360), and the final RLC data PDU 5 is received by the RLC 1210 of the E-UTRAN 1200 (indicated at 1350e).
From the standpoint of E-UTRAN 1200, the RLC data PDUs 1, 2, and 5 are received successfully (indicated at 1350a, 1350b, and 1350e), but the RLC data PDUs 3 and 4 are not received by the MAC/PHY 1220 (indicated at 1350c and 1350d). Therefore, the RLC 1210 needs to transmit an RLC status (control) PDU (indicated at 1400) to relay the acknowledgement (“received”) of the RLC data PDUs 1, 2, and 5 and the negative acknowledgement (“not received”) of the RLC data PDUs 3 and 4. The RLC status (control) PDU is sent (indicated at 1410a) and received by the RLC 1110 (indicated at 1420a).
After receiving the RLC status (control) PDU, the RLC 1110 needs to retransmit the RLC data PDUs 3 and 4 (indicated at 1500), and makes a data transmission request to the MAC/PHY 1120 (indicated at 1510). Because the uplink resource was stopped previously in step 1360, the MAC/PHY 1120 does not have sufficient uplink resources allocated for the data retransmission (indicated at 1520). Between the MAC/PHY 1120 of the UE 1100 and the MAC/PHY 1220 of the E-UTRAN 1200, steps 1530 through 1540 involve a Scheduling Request from the MAC/PHY 1120 to the MAC/PHY 1220 (indicated at 1530), to which the response is an uplink resource allocated by the MAC/PHY 1220 (indicated at 1540). Alternatively, the MAC/PHY 1220 may allocate the uplink resource in response to a Buffer Status Report (indicated at 1550 and 1560). When the MAC/PHY 1120 notes that the uplink resource has been allocated (indicated at 1600), it will send a confirmation signal to the RLC 1110 to confirm that data retransmission for RLC data PDUs 3 and 4 may begin (indicated at 1610).
During the time consumed by sending Scheduling Request and Buffer Status Report by the MAC/PHY 1120 and waiting for uplink resource allocation from the MAC/PHY 1220 (indicated at 1530 through 1560), the RLC 1110 must wait for the data transmission confirmation (indicated at 1610) before it may begin retransmitting the RLC data PDUs 3 and 4 (indicated at 1620a-b) to the RLC 1210 of the E-UTRAN 1200 (indicated at 1630a-b).
FIG. 3 shows an exemplary signaling diagram 3000 illustrating a downlink data transmission from an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) to a User Equipment (UE) in an LTE system, according to the current convention. Using substantially the same UE 1100 and E-UTRAN 1200 (and their components) as originally introduced in FIG. 1, the downlink data transmission interaction of FIG. 3 begins with the RLC 1210 of the E-UTRAN 1200 transmitting RLC data PDUs 1-5 (indicated at 3330). The RLC 1210 sends the RLC data PDUs 1-5 (indicated at 3310a-e) through the MAC/PHY 1220, the MAC/PHY 1120 to the RLC 1110. In this example, the RLC data PDUs 1, 3, 4, and 5 are received successfully (indicated at 3320a, 3320c, 3320d and 3320e), but the RLC data PDU 2 is not received by the RLC 1110 (indicated at 3310b). The RLC data PDU 5 also includes polling, signifying the end of transmitted data (indicated at 3320e).
Because of the missing RLC data PDU 2, the RLC 1110 initiates a transmission of an RLC status (control) PDU (indicated at 3400) and sends a data transmission request to the MAC/PHY 1120 (indicated at 3410). After receiving the data transmission request, the MAC/PHY 1120 notes that there is no sufficient uplink resource allocated for transmitting the RLC status (control) PDU (indicated at 3420) and thus sends a Scheduling Request (SR) to the MAC/PHY 1220 of the E-UTRAN 1200 (indicated at 3430). In response to the Scheduling Request, the MAC/PHY 1220 allocates an uplink resource to the MAC/PHY 1120 (indicated at 3440). Alternatively, the MAC/PHY 1220 may allocate the uplink resource in response to a Buffer Status Report sent by the MAC/PHY 1120 (indicated at 3450 and 3460). Once the uplink resource is allocated (indicated at 3500), the MAC/PHY 1120 confirms that data transmission is ready to the RLC 1110 (indicated at 3510) so that the RLC 1110 begins sending the RLC status PDU (indicated at 3520) through the MAC/PHY 1120, the MAC/PHY 1220 to the RLC 1210 of the E-UTRAN 1200 (indicated at 3530). In response to the RLC status PDU, the RLC 1210 retransmits the originally missing RLC data PDU 2 to the RLC 1110 of the UE 1100 (indicated at 3540 to 3560).
Once more, the time is consumed by sending Scheduling Request and Buffer Status Report by the MAC/PHY 1120 and waiting for uplink resource allocation from the MAC/PHY 1220 (indicated at 3430 through 3460), and the RLC 1110 of UE 1100 must wait for confirmation to send its RLC status PDU to the E-UTRAN 1200.
As illustrated in FIG. 1 and FIG. 3, it is understood that the dynamic resource allocation has the drawback that UE has to request for transmission resources and wait for the uplink resource allocation if no sufficient radio resources are allocated by E-UTRAN, and this causes a delay before its data can be transmitted, slowing down the overall communication between the UE and the E-UTRAN.